This invention relates to displacement sensing transducers and, more particularly, to such a transducer especially well suited to measure low pressure differentials.
One type of displacement transducer in common use utilizes strain gauges mounted on a flat flexible diaphragm. The periphery of the diaphragm is attached to a rigid support, leaving the interior of the diaphragm free to deflect. The strain gauges are oriented on the surface of the diaphragm so as to sense radial strain as the diaphragm deflects and connected in an electrical bridge to generate an output signal related to the strain in the diaphragm and thus its displacement.
A principal application of the described transducer is to measure pressure differentials in a so-called .DELTA.P cell. A typical cell design encapsulates the flat strain gauge bearing diaphragm in an oil medium between two isolation diaphragms having annular corrugations. The isolation diaphragms, which have a much lower spring constant than the flat strain gauge bearing diaphragm, serve to transmit forces resulting from the pressure differential to be measured to the latter diaphragm for transduction without affecting its response. The lower measurement limit of the described .DELTA.P cell is a pressure differential in the order of 8 to 15 psi.